New roof

[JackofAll]

Hi all,

First time poster here. Am currently renovating a mid terraced house with an extension. There is a mono pitch roof with an 11deg pitch and flat tiles( i know its mad) approx 25x17'. We would like to re-roof(possibily fit some roof lights)but cannot go higher to increase the pitch. Currently there are a few water stains on ceiling hence reason to re-roof. Could the roof be converted to a flat roof or am I mad? If so what is the best covering bearing in mind we don't have telephone numbers to play with.

[Ian]

27 minutes ago, JackofAll said:

Hi all,

First time poster here. Am currently renovating a mid terraced house with an extension. There is a mono pitch roof with an 11deg pitch and flat tiles( i know its mad) approx 25x17'. We would like to re-roof(possibily fit some roof lights)but cannot go higher to increase the pitch. Currently there are a few water stains on ceiling hence reason to re-roof. Could the roof be converted to a flat roof or am I mad? If so what is the best covering bearing in mind we don't have telephone numbers to play with.

As far as I know you can't get a normal interlocking concrete or clay tile that is okay at such a shallow pitch.

These kind of interlocking metal roof tiles in the links below can work at pitches as shallow as 10 degrees so should be okay on your roof. They need venting below the sheets btw.

Also, I wouldn't use this type of coated steel roof sheet in locations next to the sea due to corrosion issues (aluminium versions would be okay)

 https://www.metrotile.co.uk/tile-profile/roman/

https://www.roofingsuperstore.co.uk/product/corotile-lightweight-metal-roofing-system-charcoal.html

Edited July 3, 2018 by Ian

[Ian]

for the rooflights Velux do a low pitch flashing (min 10 degrees):

https://www.roofingsuperstore.co.uk/browse/pitched-roof-windows/velux-flashings/velux-low-pitch-flashing.html

[PeterW]

You can use the Nulok system on a very low pitch. @recoveringacademic Is currently installing and @Paul Stevenson will be able to give you some pointers. 

[Paul Stevenson]

Hi @PeterW yes you can use Nulok as low as a 5 degree pitch by using a 0.5mm galvanised sheet to cover the rafters or trusses in place of felt or breathable membrane and then the Nulok system on top

[JackofAll]

Thanks guys, I was not aware of the roofing options you mentioned. The nulok is something that interests us, there is currently no insulation in the roof so I am guessing we would have to fit between the rafters like recoveringacademic. Just wondering what the roof build up would consist of from outside in then, tile(nulok) galvo sheet 50mm vent gap? Insulation? Would condensation still accumulate on insulation side of galvo sheet?

 

JackofAll

[Ian]

2 hours ago, Paul Stevenson said:

Hi @PeterW yes you can use Nulok as low as a 5 degree pitch by using a 0.5mm galvanised sheet to cover the rafters or trusses in place of felt or breathable membrane and then the Nulok system on top

@Paul Stevenson

Thanks for the info. 

I have a few questions if you don't mind?

• If using Nulok in a 'warm' roof build-up using the 0.5mm galv sheet, is the Nulok recommendation to also ventilate below the galv sheet? (If there's no ventilation it's putting a lot of reliance on the integrity of the vapour barrier on the warm side of the roof build-up.)
• Are you able to offer a condensation risk analysis as part of your service when Nulok is used with the galv sheet underlay in these low-pitch situations.

The reason that I'm asking is that BS5250 :2011 which deals with condensation risk in buildings states the following:

Quotes:

"Ventilation should be provided to any void which occurs beneath any impermeable layer placed on the cold side of any thermal insulation. Ventilation paths should remain unobstructed during the life of the building; particular attention should be paid to ensuring air flow paths are maintained at changes in roof slope, and at details such as penetrations and abutments or fire break walls."

 

"Where the external covering of a roof consists of fully supported sheet metal, there is a risk that interstitial condensation will occur on the underside of the metal, which can lead to corrosion; to reduce that risk, a vapour diffusion layer should be provided immediately beneath the sheet metal."

 

"Warm pitched roof with HR underlay In roofs with an HR underlay (Figure H.4), whatever form of external covering or ceiling is provided, there is a risk of interstitial condensation forming on the underside of the HR underlay; to avoid that risk, an AVCL should be provided on the warm side of the insulation, and ventilated voids should be formed between the underside of the underlay and the insulation. Each void should be at least 25 mm deep and be vented at both high and low level."

 

[Paul Stevenson]

Hi @IAMJAMESMANNION

 

Thanks for the question

The galvanised sheet is only used on pitched roofs below 17 degrees and when you use it you do not require membrane as it replaces the membrane 17 degrees or above membrane is used. The roof is ventilated with an over fascia vent and the galvanised sheets finish over these as if you were putting on membrane. If the pitch on your roof is above 17 degrees you will not require the galvanised sheet they are used to allow very low pitches to be achieved. Hopefully this is clear if not please send me a message